In recent years there has been an increased awareness of the need for biocompatible materials for medical devices. Currently medical devices are typically made from synthetic polymeric materials such as polyvinylchloride (PVC), polyurethanes (PU), polybutadienes (latex), polyamides (PA) and others. It has also been recognized that hydrophilic materials offer good biocompatibility to medical devices when in-contact with biological fluids or living tissue. These hydrophilic materials significantly reduce adsorption of proteins and of cellular components such as platelets, leucocytes, erythrocytes and fibroblasts, and also reduce activation of intrinsic and extrinsic blood clotting pathways.
In addition to the biocompatibility of the material, the lubricity of the coating is also important, as it minimises patient trauma, and allows ease of insertion and removal of the device. An example of an important application of a biocompatible lubricious hydrophilic material is during chest drainage, which occurs after cardio-thoracic surgery. In this chest drainage procedure, preformed blood clots and whole blood is able to slide down the medical device such as thoracic drain catheter. This is achieved because of the lubricious (slippery) nature of the coated device. A biocompatible lubricious hydrophilic medical device can be used in other wound drain applications.
It has been well recognized that polyethylene oxide (PEO) (also called polyethylene glycol or PEG) when bound to a medical device offers good biocompatibility, lubricity and hydrophilicity. U.S. Pat. No. 4,424,311 discloses a polymerizable PEO monomer having polyethylene oxide unit with a carbon-carbon double bond which is grafted on to PVC or vinyl chloride-vinyl acetate copolymer or vinyl chloride-vinyl acetate-ethylene terpolymer. Disadvantages of grafting PEO are that it is a lengthy procedure and the grafted PEO units are unevenly distributed. Therefore, homogenous coverage on the surface is not achieved, which results in reduced biocompatibility and lubricity.
In another U.S. Pat. No. 5,075,400, PEO containing a polymerizable carbon-carbon double bond is polymerised, in toluene, with methyl methacrylate or ethyl methacrylate. The resultant polymer, which is referred to as supersurfactant, is predominantly water soluble and is adsorbed onto various polymeric surfaces from water, water/ethanol mixtures, or ethanol. A disadvantage of these polymers is that they act as surfactants, are adsorbed on to the surface and therefore would be readily de-sorbed from the surface when they are in contact with biological fluids such as blood, as blood has surfactant properties. Similarly, the lubricious properties would also be lost since the adsorbed surfactant is not stable on the surface. Another disadvantage is that the polymer supersurfactant is synthesized by solution polymerization in toluene and as a result high molecular weight polymer containing PEO would be difficult to produce, since PEO polymers have limited solubility in toluene.